1. Field of the Invention
The present invention relates to a personal computer for performing charge control of batteries having different capacities and switching control of a plurality of battery packs.
2. Description of the Related Art
In recent years, various types of portable, battery-driven personal computers have been developed. When such a personal computer is used with an AC adapter or a built-in battery, an operating power supply state must always be monitored, and all failures caused by abnormal power supply states must be eliminated.
A battery pack having a plurality of units each consisting of a primary battery (dry battery) and a secondary battery (rechargeable battery) is employed as a power supply for driving a lap-top computer or the like. When a battery is used as a power supply, in order to assure an operation of electronic equipment, the power level of the battery must be detected to perform battery replacement control and battery charge control for charging timings of the battery. A terminal voltage, a charge current, or discharge current of the battery is detected, the detected value is compared with a rated value of the battery, and battery charge control is performed on the basis of the comparison result. These control operations, however, are realized by a circuit entirely constituted by hardware.
Since charge control is performed by only hardware, batteries used must be limited to a specific type of battery. The rated value of the battery must be a fixed value based on the battery characteristics. When batteries having different charge and discharge characteristics are used, charge control, remaining battery capacity computation, and low-battery detection cannot be accurately performed. Charge control corresponding to types of batteries cannot be performed. For example, when a nickel-hydrogen battery compatible with a nickel-cadmium battery and having a larger capacity than the nickel-cadmium battery is to be used in electronic equipment having a characteristic value of the nickel-cadmium battery, charging and discharging of the nickel-hydrogen battery are controlled on the basis of the characteristic value of the nickel-cadmium battery, and the performance of the nickel-hydrogen battery cannot be sufficiently maximized.
A relatively inexpensive low-capacity battery and a relatively expensive high-capacity battery cannot be selectively used in such systems. When charge control is performed in accordance with the types of batteries, a circuit arrangement constituted by only hardware is undesirably complicated.
A power supply controller monitors a voltage of a battery used to supply power. When the monitored battery voltage is lowered to a voltage which does not allow supply of enough power to operate a computer, this battery is determined to have a low-battery state. When the battery voltage reaches a predetermined voltage slightly higher than a voltage corresponding to the low-battery state, an alarm is generated to signal a low battery voltage level to a user.
When a battery in the low-battery state is slightly charged, a conventional power supply controller determines that the slightly charged battery is not set in a low-battery state, thereby performing power supply control of the battery.
when the battery in the low-battery state is, however, used upon slight charging, the battery voltage is abruptly lowered, and the battery is set soon in the low-battery state. Therefore, the computer power supply is cut off without generating the alarm. In a computer having a resume function, the computer is powered off before resume processing is completed. Therefore, the resume function cannot be sufficiently utilized.